28 MICROSCOPY FOR BEGINNERS. 



length by one in width. Some microscopists use and 

 recommend them two and one-half inches long by one- 

 half an inch wide, and this will probably be the size of 

 the slides accompanying the student's stand. They are, 

 however, much too small ; it will be better for the be- 

 ginner to at once select the standard, three inches by 

 one inch, size. These can be bought, and the writer 

 would advise that they should be, as the edges will then 

 be ground smooth and perhaps polished, although the 

 last is not necessary. Slips can be cheaply cut by any 

 glass-dealer who has a diamond or glass-cutting wheel, 

 and if thus made, the best, whitest, smoothest, and thin- 

 nest glass should be selected. The rough edges of the 

 home-made slips, however, are not pleasant to handle, 

 the student who uses them taking the risk of cut fin- 

 gers. Otherwise, unless they have a green color, they 

 are as useful as the more expensive ones sold by the 

 dealers. 



A drop of water on a slip of smooth glass is not easi- 

 ly kept in position. "When the slide is placed on the 

 stage, and the microscope is inclined for use, the water 

 will surely run away, and probably carry the object with 

 it. If the microscope is not inclined, the convex sur- 

 face of the drop, and its tremulous movements, will so 

 affect the light that the image will be distorted, and the 

 observer will obtain erroneous impressions. A piece of 

 glass placed over the water will flatten the surface, the 

 distortion of the image will be partially counteracted, 

 and capillary attraction will keep the liquid from en- 



